The present invention relates to piezoelectric transducers and in particular to acoustic antennas which can be immersed to a great depth. The specific field of the invention is the construction of transmitting and receiving transducers and antennas employed in underwater acoustics.
The construction of piezoelectric transducers and acoustic antennas which are to be immersed to a great depth raises problems as to the mechanical strength of the air-tight housings and coverings containing the transformers as well as problems caused by variations in the properties of the piezoelectric elements when they are subjected to non-isotropic hydrostatic pressures. A solution, which consists of placing the air contained in the housing cover under the same pressure as the exterior, is already known.
Aside from elementary transducers composed of a single piezoelectric motor element contained in an individual housing, there are also known multimotor transducers composed of a plurality of piezoelectric motor elements located within the same cylindrical envelope and of antennas composed of a plurality of juxtaposed multimotor transducers. The construction of these multimotor transducers and of these antennas raises problems when they must be immersed to a great depth since a large volume of air, not occupied by the motor elements, remains within the envelope. Placing the volume of air in pressure equilibrium with the outside by means of a deformable balloon is not a practical solution since it would be necessary to use deformable containers of very large volume.
An object of the present invention is to provide means which make it possible to immerse at great depth elementary transducers and antennas composed of a plurality of motor elements located in the same envelope, without detrimentally affecting the properties of the piezoelectric elements.
The invention is applicable either to elementary transducers having their own envelope or to transducers and antennas composed of a plurality of motor elements located within the same water-tight envelope. In this latter case, they apply to antennas composed of a cylindrical envelope which serves as a vibrating wall against which there are radially arranged piezoelectric motor elements which may either have no point of contact with each other or else be connected by a central countermass. The invention may also be used in the case of antennas composed of a plurality of piezoelectric motor elements which are mounted in a star shape around a common central countermass, the horns of which have the shape of cylindrical segments and are juxtaposed so that they define a cylindrical surface. In general, the present invention applies to all piezoelectric transducers and to all antennas comprising on the one hand a gas-tight envelope and on the other hand at least one piezoelectric motor element located partially within the envelope and constituting a part of the walls thereof, called the vibrating wall, which transmits the acoustic waves between the water and the piezoelectric motor elements.